Scientific advisers to the government have warned of the risk of lifting the lockdown in England, as the UK begins the final weekend before rules change.
Professor John Edmunds said it was a “political decision” to ease measures; Sir Jeremy Farrar said the NHS test and trace system should be “fully working”.
From Monday schools will reopen and up to six people can meet in England, with other nations also easing measures.
Police have urged people not to break social distancing rules this weekend.
The Scientific Advisory Group for Emergencies (Sage), which advises the government, has published details of its confidential meetings.
It includes minutes of 34 Sage sessions, going back to 22 January, and a series of scientific reports.
They show one Sage meeting on 23 April estimated there would be only 1,000 cases per day by mid-May.
Instead, estimates by the Office for National Statistics suggest there are currently 8,000 cases per day in England alone. Those figures do not include cases in care homes or hospitals.
Prof Edmunds, from the London School of Tropical Hygiene and Medicine and a member of Sage, said the levels of coronavirus were still “very high” and many scientists would rather the number of cases declined before measures were relaxed.
Sir Jeremy Farrar, director of the Wellcome Trust and a member of Sage, said on Twitter that Covid-19 is “spreading too fast to lift lockdown in England” and NHS test and trace “has to be fully working and infection rates have to be lower”.
Speaking on BBC Radio 4’s Today programme, Prof Peter Horby, who sits on Sage and chairs its NERVTAG subcommittee, agreed, saying the R number was still close to one and it was important we “don’t lose control”.
“What I would say is that returning to a situation where we lost control again is far worse than another week or two of social measures,” he said.
A fourth Sage member, Prof Calum Semple, said a “brave” political decision had been made to coincide with when schools were due to reopen “were everything normal”, but warned that high levels of transmission were still being seen.
“Essentially we’re lifting the lid on a boiling pan and it’s just going to bubble over,” he said. “We need to get it down to simmer before we take the lift off, and it’s too early.”
The Sage documents warned there would be “little time” to reimpose stricter lockdown measures if the infection rate started to creep up again.
Epidemiologist Prof Sian Griffiths told BBC Breakfast that if scientists were in charge of decisions, lockdown would probably not be eased currently, but she said there were other factors to consider.
“I would say there is a huge amount of stress and strain which goes along with not being able to see your friends and your family and that to be able to see them, albeit at a distance, may actually help people’s mental health and may help them live with lockdown better and may help them comply better,” she said.
Prof Sally Bloomfield, of the London School of Hygiene and Tropical Medicine, warned against having a barbecue with guests, saying the virus could be present on bottles, cutlery and other objects. Picnics where people brought their own food were a better option, she said.
Greater Manchester mayor Andy Burnham also said it was a “dangerous moment” and said the easing of the lockdown was “premature” as he called on the government to reveal the regional R number so that the public can judge the level of risk.
It comes as police forces in England have warned people to take care in busy areas and beauty spots and as a fine weekend of weather is forecast.
Each of the UK’s nations has a different approach – and timescale – to lifting the lockdown on Monday.
England is the only nation to reopen primary schools to selected year groups on Monday and will allow groups of up to six to meet outside.
In Scotland, two separate households – up to a maximum of eight people – can meet outdoors and in Northern Ireland, groups of up to six people who do not live together can meet outdoors.
In Wales, any number of people from two different households will be able to meet each other outside from Monday, but beauty spots will remain closed.